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Central PA - December 2013


PennMan

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I don't know what NAM you're looking at. The one I'm seeing has MUCH more than 1-3 inches, at least based on a cursory glance.

 

Definitely an improvement

 

12z:

post-300-0-57409100-1386276201_thumb.png

 

18z:

post-300-0-53042700-1386275903_thumb.png

 

This is BEFORE the main batch of precip even starts. Maybe there's a brief warm up near 850mb at the beginning of the main batch (around hr 30, Twisterdata hasn't quite loaded that hour yet), but then it cools again immediately thereafter. That looks great to me.

 

EDIT: Twisterdata gave me the wrong hour on the 12z. It's been fixed.

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Is that the Euro on Wundermaps? 

 

BTW for future ref, Wundermaps seem to be pretty good with snow.

Thats what someone else posted it as, so Im not quite sure. I am assuming that it is the latest snow map from the Euro. So what is the Euro seeing that the NAM isn't regarding snow further south?
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Other than a brief snow/sleet mix around hour 30, most of it is snow in State College. With QPFs near an inch, that's more than 1-3 inches.

 

The NAM is likely overdoing the precip as usual, but WRT temperatures, it has support (now) from the Euro, etc. I'm definitely thinking this could be a good event here in State College.

 

post-300-0-21177200-1386276360_thumb.png

 

post-300-0-81153800-1386276370_thumb.png

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Still appears to be a bit of a warm layer at 00z Saturday; the thermal gradient is so tight, it depends on exactly where you plot the sounding. This spot seemed to be the best approximation for KUNV, several miles to the northeast.

 

 

Fair point. The gradient is REALLY tight, so model interpolation is going to be the best we have. That being said, I don't think this is the coldest NAM run we're going to see, either. It's probably going to trend a bit colder from here on out (towards the Euro).

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CTP snowmap has <1" for my area while CTP grids for Friday night continue to say snow, maybe mixed with sleet and zr..turning to all snow after 10pm with a half to three quarters of QPF. Same thing for places like Johnstown and State College. Somethins gotta give there, they should be issuing their afternoon updates shortly. 

 

 

Thoughts?

 

The Euro has continued to be the most supportive model for a sizable snowfall in most of Central PA vs the other models that focus more on Western/NW PA. AccuPro's 3D cross section product helps alot with visualizing the progression of the cold air. I wish I could post a pic of it but thats a big no no. Taking a cross section from Pit across the state to Allentown using the Euro shows that the cold air undercuts west to east from about 850mb and lower first initially leaving the relatively warm layer from 850 to 700mb that has been discussed about. However that particular layer is cold enough (barely) to support snow all through the column when it counts at hours 36 and 42 for the central areas...probably at the expense of good snow ratios. Cold enough air at those levels don't quite get to the Sus Valley in time for very much snow, although the 0ºC isotherm is undercutting at about 925mb. This warmer layer between 850-700mb also makes for higher 1000-500mb thickness and thus you can't really use the traditional 540 line to place the rain/snow line. The 546 line might be a better one to use in this instance. 

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Fair point. The gradient is REALLY tight, so model interpolation is going to be the best we have. That being said, I don't think this is the coldest NAM run we're going to see, either. It's probably going to trend a bit colder from here on out (towards the Euro).

 

Definitely a decent chance of that happening, especially with the 12z Euro a hair colder than 00z over central PA.

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